Thixotropic investment material



Patented Nov. 28, 1950 THIXOTROPIC INVESTMENT MATERIAL Elbert E. Ensign,Ypsilanti, Mich., assignor to Ford Motor Company, Dearborn, Mich., acorporation of Delaware No Drawing. Application October 7, 1947, SerialNo. 778,469

4 Claims. 1

This application is concerned with the foundry molding art and moreparticularly with a process for the precision casting of metals by theinvestment or lost wax process. Basically this process depends upon theuse of a destructible pattern constructed of wax, low melting pointmetal, combustible or soluble material. Such a pattern is surrounded orinvested in a hardenable mixture which is then permitted to set orharden. The mold so prepared and containing the pattern is then treatedto remove the pattern. If wax is chosen as the pattern material it canbe removed by gentle heating to melt the wax. A similar treatment can beapplied to low melting metal patterns. The combustible or solublepatterns can be removed by heating or dissolving. The choice of patternmaterial for any particular use is dictated by considerations well knownto those skilled in the art and need not be elaborated upon here.

There are many satisfactory investment materials for the lower meltingalloys and metals such as pewter, aluminum, bronze, brass, etc. However,attempts to extend the use of investment casting to steel have met withonly limited success because of the lack of a really satisfactoryinvestment material. Such a material must be strong and thermally stableto give a faithful reproduction of the original pattern. In addition, itmust be sufliciently refractory to remain in contact with molten steelat temperatures circa 3000 F. without fusing or gassing and must underthese high temperatures impart to the metal a smooth surface. Inaddition to the above, a commercially successful investment materialmust be fairly cheap if precision casting is to be competitive withother methods of fabrication.

To date the most widely used investment molds for use with steel havecontained silica obtained from the hydrolysis of ethyl silicate or otherorganic ester of silicic acid; While such organosilica compounds didyield satisfactory castings,

they are objectionable commercially because of To provide such aninvestment material for use in ferrous casting, applicant has takenadvantage of the thixotropic properties of zeolitic materials, eithernatural or synthetic. When properly prepared these zeolitic investmentmaterials have the property of remaining plastic indefinitely as long asthey are kept agitated and the loss of moisture is prevented. Thus largebatches of investment material may be prepared in advance and used asrequired.

While natural zeolitic materials may be used in the manufacture ofapplicant's investment material, considerations of economy, convenienceand reproductibility of results dictate the use of the syntheticmaterials. Silica flour which is a form of very finely divided silica isthe base material employed in the manufacture of the synthetic zeolite.To such silica flour is added water, an acid, a source of aluminum ionsand a source of sodium and/or potassium ions. The following is aspecific example of a method for preparing a successful investmentmaterial. A solution was prepared comprising:

Per cent Water 83.5 Sodium Phosphate 6.6 Potassium alum 3.4 HydrochloricAcid 22 B 6.5

One part of this solution was mixed with three parts of fine silicaflour and intensively agitated at room temperature. Under theseconditions a reaction took place to yield a plastic, synthetic zeolite.The proportions given are by way of i1- lustration only and representonly one of an endless series of mixtures which can be employed for thesame purpose. For example, ordinary sodium chloride can be employedinstead of the sodium phosphate. Apparently it is only essential that asource of acid, aluminum ions and sodium and/ or potassium ions beadded. However, the anions used should be selected with regard to theirbehavior during the firing and subsequent pouring of the mold.

The use of applicants thixotropic zeolitic investment materials requiresno variation from previously developed techniques based upon the use oforganic silicates. The only precaution to be observed is the constantagitation of the zeolitic material to prevent setting. The unusedzeolite should, of course, be protected from loss of moisture.

What is claimed is:

l. The process of preparing a thixotropic investment material comprisingmixing by weight 83.5 parts of water, 6.6 parts of sodium phosphate, 3.4parts of potassium alum, 6.5 parts of 22 B. hydrochloric acid, adding tothe solution so formed three times its weight of fine silica flour, andintensively agitating the mix at room temperature.

2. The process of preparing thixotropic investment molding materialcomprising mixing an aqueous solution containing a soluble acid and asoluble aluminum compound and a soluble compound chosen from the groupconsisting of sodium and potassium compounds with sufficient silicaflour to give a molding material of the desired consistency andintensively agitating the mix.

3. The process of preparing a thixotropic investment molding materialcomprising mixing an aqueous solution containing a soluble acid, asoluble aluminum compound and a soluble sodium compound with sufficientsilica flour to give a molding material of the desired consistency.

4. The process of preparing a thixotropic investment molding materialcomprising mixing an aqueous solution containing a soluble acid,

4 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,052,514 Poulson Feb. 11, 19131,756,623 Behrman Aug. 29, 1930 1,872,183 Porter Aug. 16. 1932 1,889,007Wallace Nov. 29, 1932 2,193,346 Ruddle Mar. 12, 1940 2,213,530 MonteroSept. 3, 1940 2,233,701 Grossman Mar. 4, 1941 2,237,592 Dunbeck Apr. 8,1941 2,237,593 Dunbeck Apr. 8, 1941 2,256,456 Dietert Sept. 16, 1941OTHER REFERENCES American Foundryman, April 1947, page 36.

20 (Copy in Division 3.)

and soluble aluminum compound and a soluble 25 and their PhysicalProperties. by C. S. Ross and potassium compound with sufficient silicaflour to give a molding material of the desired consistency.

ELBERT E. ENSIGN.

Earl V. shamon, pages 88-90.

2. THE PROCESS OF PREPARING THIXOTROPHIC INVESTMENT MOLDING MATERIALCOMPRISING MIXING AN AQUEOUS SOLUTION CONTAINING A SOLUBLE ACID AND ASOLUBLE ALUMINUM COMPOUND AND A SOLUBLE COMPOUND CHOSEN FROM THE GROUPCONSISTING OF SODIUM AND POTASSIUM COMPOUNDS WITH SUFFICIENT SILICAFLOUR TO GIVE A MOLDING MATERIAL OF THE DESIRED CONSISTENCY ANDINTENSIVELY AGITATING THE MIX.